Excessive B cell activity and loss of regulatory cells occurs in patients with active SLE; these abnormalities are less marked when the disease is quiescent. Nevertheless, excessive B cell proliferation occurs even in inactive patients. Loss of a subpopulation of regulatory T cells occurs in patients with active SLE. Antibodies to the precursors of suppressor T cells are spontaneously produced by the patients. Such antibodies prevent normal T cell control of abnormal B cell activity allowing perpetuation of autoantibody production. Studies with monoclonal anti-T cell antibodies indicate that many patients have abnormal presence of activated T cells and increased numbers of B cells. Study of a large number of patients with SLE indicates that SLE is not a disease, but a syndrome with different cellular bases.